(1) Field of the Invention
The present invention relates to a system and method for controlling a damping force characteristic of a shock absorber (hereinafter referred to as a damper) installed between an unsprung mass and a sprung mass of an automotive vehicle.
(2) Description of the Background Art
Japanese Utility Model Registration Application Publications No. Showa 80-47612 and No. Showa 61-110412 exemplify systems for controlling damping force coefficients of dampers.
The former disclosed damping force characteristic controlling system determines a road surface condition on the basis of a data of a distance from the damper position to the ground, i.e., road surface derived from a distance sensor and controls its damping force according to the road surface condition.
The latter disclosed damping force characteristic controlling system detects peak position values of a piston member of the damper at an expansion stroke side and compression stroke side of the damper on the basis of a displacement of the damper position and controls the damping force to become samller when the peak position values fall in a neutral range of a predetermined width with a neutral position of a relative displacement of the damper as a center. Then, in the latter disclosed damping force controlling system, the width of the neutral range is varied according to a vehicle speed so that a delay in a control timing for changing the damping force characteristic is considerably reduced.
However, the former damping force controlling system requires the distance sensor so that the system structure becomes accordingly complex and cost of manufacture of the system becomes increased.
In addition, in the latter controlling system, the delay in the control timing while the vehicle is running at high speeds, is reduced by the change in the width of the neutral range according to the vehicle speed. However, the latter disclosed damping force controlling system provides a rising delay of applying the changed damping force or its response delay so that the inherent control delay cannot completely be eliminated.